1. Field of the Invention
This invention relates to a semiconductor fabrication equipment, and more particularly to a rinsing system used in a photoresist coater with capability to avoid a reversed pressure effect.
2. Description of Related Art
Photolithography plays an essential role in semiconductor fabrication. All semiconductor devices need several photolithography process to transfer desired patterns so as to form the devices as designed. A semiconductor device usually includes, for example, a transistor structure with proper doping regions, a capacitor, and an interconnecting structure for connection between each component. All these needs several different photolithography processes. A more complex structure accordingly needs more photolithography processes.
The detailed photolithography technology is usually complicated but its theory is straightforwardly simple. Generally, a photoresist layer is coated on a device substrate surface, on which a device is fabricated. The photoresist layer then is exposed by a light source through a photomask, which carries a pattern to be transferred onto the device substrate surface. The photoresist layer includes photo-sensitive material that can be exposed to light to selectively change its material property. After development, the remaining photoresist layer on the device substrate surface forms the desired pattern. The desired pattern therefore is transferred to the device substrate. Up to this stage, the photolithography process is done. A subsequent process, such as etching or doping, are performed to form one sub-structure of the device, which usually includes several different sub-structures. So, a more complex structure accordingly needs more photolithography processes.
The photoresist layer are usually formed by a spin coating process so as to obtain its thickness uniformity and adhesion without defects. After the photoresist layer is formed over a substrate, in order to conveniently move the substrate, a portion of the photoresist layer is rinsed away so as to leave a place to be clipped by moving machine. Usually, the brim of the photoresist layer is necessarily rinsed away or even the back-side of the substrate is also rinsed. An OK-82 solvent is a typical solvent for the purpose of rinse.
FIG. 1 is a schematic architecture of a conventional rinsing system used in a photoresist coater. In FIG. 1, a solvent container 10 contains OK-82 solvent. The solvent is transported to a solvent distributor 12 through a duct 11. The solvent distributor 12 has several distribution ducts 13, 14, 15, 16, 17, and 18, all of which are identical. The distribution ducts 17 and 18 are, for example, used for descriptions. On the distribution duct 17, there is a pump 19 used to transport solvent to a substrate 24 to rinse the brim of a photoresist layer (not shown) on the substrate 24, which is held by a spinner 23. The distribution duct 17 also has a filer 20, which is located before the pump 19, used to have a pure solvent without particles. Solvent is thereby transported to a duct end 22 to rinse the brim or the backside of the substrate 24.
When the pump 19 is activated, an inner cylinder 25 of the pump 19 provides a transporting force of solvent. Inside the pump 19, there are two valves corresponding to an input end 26 and an output end. When solvent inside the pump 19 is pressurized, solvent flows out to the duct end 22. However, if the pumping frequency of the inner cylinder 25 is too fast, a ball-like stopper 27 of the valve at the input end 26 may not shift to the proper place in time to seal the input end 26 while solvent is pressurized. In addition, even in a case that the stopper 27 can shift to the proper place in time, the stopper 27 still may not seal the vale at the input end 26 due to a possibility of bad sealing contact. In this situation, solvent can flow backward along a reversed direction 29. This is called a reversed pressure effect. The flowing back solvent further flows back to the solvent distributor 12 and causes a problem.
Although the filter 20 has a regulating valve 30, which can be adjusted by hand, to prevent the flowing back solvent from further flowing back to the solvent distributor 12, it practically is very difficult to have a proper adjustment in time. Because the distance between the solvent distributor 12 and the filter 20 is short, the flowing back solvent may pass through the solvent distributor 12 and flows to the distribution duct 18. The flowing back solvent then passes the distribution duct 18 and rinses a substrate 35, resulting in a damage to a photoresist layer (not shown) formed on the substrate 35. If the flowing back solvent is too strong, a few of distribution ducts may be very possible affected. If the reversed pressure effect is not effectively reduced, it must cause damages to many substrates on the other distribution ducts.
In summary, because the conventional rinsing system has no effective capability to stop the flowing back solvent flowing back to the solvent distributor, the flowing back solvent can flow two other distribution ducts to cause a damage to the substrates.